U.S. patent application number 14/917350 was filed with the patent office on 2016-08-04 for heart monitoring system.
The applicant listed for this patent is MURATA MANUFACTURING CO., LTD., TURUN YLIOPISTO. Invention is credited to Markus GRONHOLM, Marika JUPPO, Tero KOIVISTO, Ulf MERIHEINA, Mikko PANAALA, Kati SAIRANEN.
Application Number | 20160220152 14/917350 |
Document ID | / |
Family ID | 51626108 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160220152 |
Kind Code |
A1 |
MERIHEINA; Ulf ; et
al. |
August 4, 2016 |
HEART MONITORING SYSTEM
Abstract
A device that includes a sensor of angular motion configured to
obtain an angular ballistograph signal indicative of rotational
movement of a chest of a subject. Signal processing means are
configured to generate from this angular ballistocardiograph signal
measured values of an output parameter, which is indicative of
cardiac operation of the subject.
Inventors: |
MERIHEINA; Ulf; (Soderkulla,
FI) ; JUPPO; Marika; (Espoo, FI) ; KOIVISTO;
Tero; (Turku, FI) ; PANAALA; Mikko; (Raisio,
FI) ; SAIRANEN; Kati; (Naantali, FI) ;
GRONHOLM; Markus; (Turku, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MURATA MANUFACTURING CO., LTD.
TURUN YLIOPISTO |
Kyoto
Turku |
|
JP
FI |
|
|
Family ID: |
51626108 |
Appl. No.: |
14/917350 |
Filed: |
September 10, 2014 |
PCT Filed: |
September 10, 2014 |
PCT NO: |
PCT/IB2014/064377 |
371 Date: |
March 8, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/113 20130101;
A61B 5/1107 20130101; A61B 5/746 20130101; A61B 2562/0219 20130101;
A61B 2562/028 20130101; A61B 5/7246 20130101; A61B 5/7282 20130101;
A61B 5/046 20130101; A61B 5/6823 20130101; A61B 5/7278 20130101;
A61B 5/1102 20130101; A61B 5/1121 20130101; G01C 19/5783
20130101 |
International
Class: |
A61B 5/11 20060101
A61B005/11; A61B 5/113 20060101 A61B005/113; A61B 5/00 20060101
A61B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2013 |
FI |
20135924 |
Claims
1. A system, characterized by including comprising: a gyroscope
configured to obtain on a chest of a subject and using Coriolis
effect an angular ballistocardiograph signal indicative of
rotational recoil movement on the chest of the subject in response
to cardiovascular rotation within the chest of the subject; and a
signal processor configured to generate from the angular
ballistocardiograph signal measured values of an output parameter
indicative of cardiac operation of the subject.
2. The system of claim 1, further comprising: a sensor unit
comprising the sensor of angular motion; and a control unit coupled
to the sensor unit to receive the angular ballistocardiograph
signal.
3. The system of claim 2, wherein the sensor unit is configured to
be attached to the exterior of the chest of the subject, and
wherein the control unit is communicatively coupled to the sensor
unit to receive the angular ballistocardiograph signal.
4. The system of claim 1, wherein the sensor of angular motion is
configured to sense rotational movement in a sense direction that
is parallel to an axis of rotation, and wherein the sense direction
of the sensor unit is configured to be aligned to a symmetry plane
of a body of the subject.
5. The system of claim 4, wherein the subject is a human and the
symmetry plane is the sagittal plane of the human subject.
6. The system of claim 2, wherein the system comprises a mobile
computing device.
7. The system of claim 2, wherein the system includes a remote
node, communicatively coupled to the control unit.
8. The system of claim 1, wherein the signal processor is
configured to generate from the angular ballistocardiograph signal
a measured value representing radial orientation of the heart,
angular velocity of the heart, or angular acceleration of the heart
during the cardiac operation of the subject.
9. The system of claim 1, wherein the signal processor is
configured to generate from the angular ballistocardiograph signal
a measured value representing temporary stroke volume of the heart
of the subject.
10. The system of claim 9, wherein the angular ballistocardiograph
signal is sequential, the signal processor is configured to
determine an amplitude of a sequence of the angular
ballistocardiograph signal, and wherein the signal processor is
configured to use the amplitude to generate a measured value
representing temporary stroke volume during the sequence of the
angular ballistocardiograph signal.
11. The system of claim 1, wherein the signal processor is
configured to generate from the angular ballistocardiograph signal
a measured value representing beat-to-beat time or heart rate of a
heart of the subject.
12. The system of claim 1, wherein the signal processor is
configured to generate from the angular ballistocardiograph signal
a measured value representing aortic closing or aortic opening of a
heart of the subject.
13. The system of claim 1, wherein the signal processor is
configured to generate from the angular ballistocardiograph signal
a measured value representing another vital operation of the
subject.
14. The system of claim 13, wherein the vital operation is
respiration.
15. The system of claim 2, wherein the control unit is configured
to store angular ballistocardiograph signals of a subject or
measured values generated from the angular ballistocardiograph
signals of the subject into a local or remote database.
16. The system of claim 15, wherein the control unit is configured
to compare new measured values to a selected piece of stored
information, and create an alarm if a deviation of new values from
the stored information exceeds a predefined threshold.
17. The system of claim 1, wherein the signal processor is
configured to determine amplitude variation of the angular
ballistocardiograph signal; and generate measured values of an
output parameter from the determined amplitude variation of the
angular ballistocardiograph signal.
18. The system of claim 17, wherein the signal processor is
configured to determine the amplitude variation from wave patterns
repeating on a heart-beat rate on the angular ballistocardiograph
signal so that the amplitude variation includes two or more
increases of the amplitude and two or more decreases of the
amplitude.
19. The system of claim 18, wherein the signal processor is
configured to determine the amplitude variation from aortic opening
(AO) wave patterns repeating on a heart-beat rate on the angular
ballistocardiograph signal.
20. The system of claim 1, wherein the signal processor is
configured to extract from a signal indicative of electromagnetic
phenomena related to cardiac activity a first wave pattern
repeating on a heart-beat rate; extract from the angular
ballistocardiograph signal a second wave pattern repeating on the
heart-beat rate; form timing data, a value of the timing data being
indicative of a time period from a reference point of the first
wave pattern belonging to one heart-beat period to a reference
point of the second wave pattern belonging to the same heart-beat
period; and use the timing data to generate measured values of an
output parameter.
21. The system of claim 20, wherein the signal processor is
configured to determine correlation between the timing data and
pacing data indicative of the heart-beat rate; and use the
correlation to generate measured values of an output parameter.
22. The system of claim 20, wherein the signal processor is
configured to determine stochastic variation in the timing value
between successive heart-beat periods; and use the stochastic
variation to generate measured values of an output parameter.
23. The system of claim 17, wherein the signal processor is
configured to use the output parameter to indicate abnormal cardiac
operation of the subject.
24. The system of claim 23, wherein the abnormal cardiac operation
results from atrial extrasystole or atrial fibrillation.
25. The system of claim 1, wherein the sensor unit is configured to
be positioned on a pectoral part of the upper torso of the
subject.
26. The system of claim 1, wherein the sensor unit is configured to
be positioned on a backside part of the upper torso of the
subject.
27. The system of claim 1, wherein the sensor unit is configured to
obtain an angular ballistocardiograph signal with a
microelectromechanical gyroscope.
28. A method, comprising: obtaining with a gyroscope on a chest of
a subject, and using Coriolis effect, an angular
ballistocardiograph signal indicative of rotational recoil movement
of the chest of the subject in response to cardiovascular rotation
within the chest; and generating from the angular
ballistocardiograph signal measured values of an output parameter
indicative of cardiac operation of the subject.
29. The method of claim 28, including: attaching a sensor unit
comprising the sensor of angular motion to the exterior of the
chest of the subject; and forwarding the angular
ballistocardiograph signal to a control unit communicatively
coupled to the sensor unit.
30. The method of claim 28, including: sensing rotational movement
in a sense direction that is parallel to an axis of rotation; and
aligning the sense direction to a symmetry plane of a body of the
subject.
31. The method of claim 30, wherein the subject is a human and the
symmetry plane is the sagittal plane of the human subject.
32. The method of claim 29, including forwarding the measured
values to a remote node, said remote node being communicatively
coupled to the control unit.
33. The method of claim 28, further comprising generating, from the
angular ballistocardiograph signal a measured value representing
radial orientation of a heart of the subject, angular velocity of
the heart, or angular acceleration of the heart during the cardiac
operation of the subject.
34. The method of claim 28, further comprising generating, from the
angular ballistocardiograph signal a measured value representing
temporary stroke volume of a heart of the subject.
35. The method of claim 45, characterized in wherein the angular
ballistocardiograph signal is sequential, and the method comprises
determining an amplitude of a sequence of the angular
ballistocardiograph signal, and using use the amplitude to generate
a measured value representing temporary stroke volume during the
sequence of the angular ballistocardiograph signal.
36. The method of claim 28, further comprising generating, from the
angular ballistocardiograph signal, a measured value representing
beat-to-beat time or heart rate of a heart of the subject.
37. The method of claim 28, further comprising generating, from the
angular ballistocardiograph signal, a measured value representing
aortic closing or aortic opening of a heart of the subject.
38. The method of claim 28, further comprising generating, from the
angular ballistocardiograph signal, a measured value representing
another vital operation of the subject.
39. The method of claim 38, wherein the vital operation is
respiration.
40. The method of claim 28, further comprising storing angular
ballistocardiograph signals of a subject or measured values
generated from the angular ballistocardiograph signals of the
subject in a local or remote database.
41. The method of claim 40, further comprising comparing new
measured values to a selected piece of stored information, and
creating an alarm if the deviation of new values from the stored
information exceeds a predefined threshold.
42. The method of claim 28, further comprising determining
amplitude variation of the angular ballistocardiograph signal;
generating measured values of an output parameter from the
amplitude variation of the angular ballistocardiograph signal.
43. The method of claim 42, further comprising determining the
amplitude variation from wave patterns repeating on the heart-beat
rate on the angular ballistocardiograph signal so that the
amplitude variation includes two or more increases of the amplitude
and two or more decreases of the amplitude.
44. The method of claim 43, further comprising determining the
amplitude variation from aortic opening (AO) wave patterns
repeating on a heart-beat rate on the angular ballistocardiograph
signal.
45. The method of claim 28, further comprising: extracting from a
signal indicative of electromagnetic phenomena related to cardiac
activity a first wave pattern repeating on a heart-beat rate;
extracting from the angular ballistocardiograph signal a second
wave pattern repeating on the heart-beat rate; forming timing data,
a timing value of the timing data being indicative of a time period
from a reference point of the first wave pattern belonging to one
heart-beat period to a reference point of the second wave pattern
belonging to the same heart-beat period; and using the timing data
to generate measured values of an output parameter.
46. The method of claim 45, further comprising: determining a
correlation between the timing data and pacing data indicative of a
heart-beat rate; using the correlation to generate measured values
of an output parameter.
47. The method of claim 46, further comprising determining
stochastic variation in the timing value between successive
heart-beat periods; and using the stochastic variation to generate
measured values of an output parameter.
48. The method of claim 42, further comprising using the output
parameter to indicate abnormal cardiac operation of the
subject.
49. The method of claim 48, wherein the abnormal cardiac operation
results from atrial extrasystole or atrial fibrillation.
50. The method of claim 29, further comprising positioning the
sensor unit on a pectoral part of an upper torso of the
subject.
51. The system of claim 29, further comprising positioning the
sensor unit on a backside part of the upper torso of the
subject.
52. The system of claim 29, further comprising obtaining the
angular ballistocardiograph signal with a microelectromechanical
gyroscope.
53. A computer program product embodied on a non-transitory
computer-readable medium, said computer-readable medium encoding
instructions for executing the method of claim 28 in a cardiac
monitoring system, when run on a computer.
54. A system, comprising: gyroscope means for obtaining on a chest
of a subject, and using Coriolis effect, an angular
ballistocardiograph signal indicative of rotational recoil movement
on the chest of the subject in response to cardiovascular rotation
within the chest of the subject; and signal processing means for
generating, from the angular ballistocardiograph signal, measured
values of an output parameter indicative of cardiac operation of
the subject.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to monitoring vital signs of a
user and especially to a system, method and a computer program
product for monitoring cardiac operation of a subject, defined in
preambles of the independent claims.
BACKGROUND OF THE INVENTION
[0002] A heart is a hollow tissue formed of cells that are capable
of producing a contraction that changes the length and shape of the
cell. Heart pumps blood in cyclic contractions through a network of
arteries and veins called the cardiovascular system. As shown in
FIG. 1, a human heart includes four chambers, which are divided by
a septum into a right side (right atrium RA and right ventricle RV)
and a left side (left atrium LA and left ventricle LV). During a
heartbeat cycle, the right atrium RA receives blood from the veins
and pumps it into the right ventricle and the right ventricle RV
pumps the blood into the lungs for oxygenation. The left atrium LA
receives the oxygenated blood from the lungs and pumps it to the
left ventricle LV, and the left ventricle LV pumps the blood into
the veins. The apex AP of the heart is a portion formed by the
inferolateral part of the left ventricle LV.
[0003] Various techniques have been developed to provide measurable
parameters that are indicative of cardiac operation of a monitored
subject. Many of these techniques are invasive and therefore
suitable for advanced medical use only.
[0004] In the noninvasive side, echocardiography is a technique
that applies ultrasound to provide an image of the heart.
Echocardiography can be comfortably carried out at the bedside, and
it has therefore become a widely-used tool for noninvasive studies
on cardiac mechanics of diseased and healthy hearts. The produced
images require, however, complex and basically immobile computer
equipment and the images need to be interpreted by a highly trained
physician. Ambulatory or long-term monitoring of the cardiac
operation outside the clinical environment by echocardiography is
practically impossible.
[0005] Electrocardiography is based on measuring electrical
activity of the heart with electrodes attached to the surface of
the skin of the monitored subject. In electrocardiography, wave
depolarization of the heart is detected as changes of voltage
between a pair of electrodes placed in specific positions on the
skin. Typically a number of electrodes are used, and they are
arranged in combination into pairs (leads). Electrocardiograms are
very accurate and widely used, and also allow some computerized
interpretation. Proper placement of the electrodes may, however, be
challenging for users without medical training. In addition, the
measurement system typically requires a computerized system
connected with cables to a plurality of self-adhesive pads that
couple through conducting gel to the skin of the monitored subject.
Moving with such wiring is very limited.
[0006] Patent publication WO2010145009 discloses an apparatus for
determining information indicative of physiological condition of a
subject. The apparatus comprises a sensor device that obtains
ballistocardiograph data indicative of heart motion of the subject,
measured along a plurality of spatial axes. Ballistocardiograph
data indicates the extent of mechanical movements of a body that
take place in response to the myocardial activity of the heart.
This ballistocardiograph data is then used to process data that is
indicative of heart motion of the subject. This prior art method
overcomes some of the limitations of the prior art. However, it has
been noted that the linear measurement along spatial axes is
strongly affected by the posture of the monitored subject during
the measurement. In addition, some characteristics of the heartbeat
cycle are not completely reliably measurable with the linear motion
data.
BRIEF DESCRIPTION OF THE INVENTION
[0007] The object of the present invention is to provide a
non-invasive cardiac operation monitoring solution where at least
one of disadvantages of the prior art is eliminated or at least
alleviated. The objects of the present invention are achieved with
a system, method and computer program product according to the
characterizing portions of the independent claims.
[0008] The preferred embodiments of the invention are disclosed in
the dependent claims.
[0009] Due to a specific orientation of the myocardial fibers, in a
heartbeat cycle the heart makes rotation along its long-axis and a
wringing (twisting) motion. Torsional squeezing and opening of the
left ventricle LV caused by heart rotation stands for about 60% of
the stroke volume of the heart. The rest may be considered to
result from the deflection of a wall between the left ventricle LV
and the left atrium LA, and from the linear squeezing of the left
ventricle LV from the apex AP.
[0010] The present invention discloses a device that includes a
sensor of angular motion configured to obtain an angular
ballistograph signal indicative of rotational movement of a chest
of a subject. Signal processing means are configured to generate
from this angular ballistocardiograph signal measured values of an
output parameter, which is indicative of cardiac operation of the
subject. The generated values or parameters can be used in a
stand-alone system or in combination to improve signals and/or
analysis made in a system that applies one or more of the prior art
techniques.
[0011] The signal of a sensor of angular motion is not affected by
gravity, which makes the measurement practically independent of the
position or posture of the monitored subject. It has been noted
that the external angular motion of the chest is orders of
magnitude larger than what one would anticipate from the mere
extent of the heart rotation and the ratio between the size of the
heart and the diameter of the human chest. It has also been noted
that the detection of the angular motion is also relatively
insensitive to the location of the sensor in respect to the heart.
Due to these aspects, accurate measurements can be made with even
one gyroscope, for example microelectromechanical gyroscope,
attached to the chest of the monitored subject.
Microelectromechanical gyroscopes are accurate, small in size and
commercially well available.
[0012] These and further advantages of the invention are discussed
in more detail in the following with detailed descriptions of some
embodiments of the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0013] In the following the invention will be described in greater
detail, in connection with preferred embodiments, with reference to
the attached drawings, in which
[0014] FIG. 1 illustrates elements of a human heart;
[0015] FIG. 2 illustrates functional elements of an embodiment of a
monitoring system;
[0016] FIG. 3 illustrates functional configuration of a cardiac
monitoring system;
[0017] FIG. 4 illustrates another exemplary configuration of a
cardiac monitoring system;
[0018] FIG. 5 illustrates measurement results taken with the system
of FIG. 4;
[0019] FIG. 6 illustrates a remote monitoring system including the
cardiac monitoring system;
[0020] FIG. 7 illustrates an exemplary angular ballistocardiograph
signal during heartbeat cycles;
[0021] FIG. 8 shows a simplified example of an angular
ballistocardiograph signal;
[0022] FIG. 9 illustrates an exemplary output signal corresponding
to the angular ballistocardiograph signal of FIG. 7 after a
specific matched filtering;
[0023] FIG. 10 illustrates a potential AO peak from the signal of
FIG. 7; and
[0024] FIG. 11 illustrates exemplary values of stroke volume and
heartbeat timestamps measured from a test subject;
[0025] FIG. 12 illustrates measurements taken simultaneously from
one test subject with various measurement technologies;
[0026] FIG. 13 illustrates generation of a parameter indicative of
atrial extrasystole of the subject;
[0027] FIG. 14 shows exemplary time differences (TD) in a case of
atrial fibrillation of the subject;
[0028] FIG. 15 illustrates amplitude variation of an exemplifying
signal in a case of atrial fibrillation when a person under
consideration is breathing;
[0029] FIG. 16 illustrates an example of an ECG waveform and an
angular ballistocardiogram waveform of an exemplifying signal
indicative of cardiovascular rotation.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0030] The following embodiments are exemplary. Although the
specification may refer to "an", "one", or "some" embodiment(s),
this does not necessarily mean that each such reference is to the
same embodiment(s), or that the feature only applies to a single
embodiment. Single features of different embodiments may be
combined to provide further embodiments.
[0031] In the following, features of the invention will be
described with a simple example of a device architecture in which
various embodiments of the invention may be implemented. Only
elements relevant for illustrating the embodiments are described in
detail. Various implementations of heart monitoring systems and
methods comprise elements that are generally known to a person
skilled in the art and may not be specifically described
herein.
[0032] The monitoring system according to the invention generates
one or more output values for one or more parameters that are
indicative of operation of the heart of a subject. These values may
be used as such or be further processed to indicate condition of
the heart of the subject. The monitoring system is herein disclosed
as applied to a human subject. The invention is, however,
applicable to animal species or any type of subject that has a
heart and a body that responsively encloses the heart such that the
heartbeat results in recoil motion of the body.
[0033] The block chart of FIG. 2 illustrates functional elements of
an embodiment of a monitoring system 200 according to the present
invention. The system includes a sensor of angular motion
configured to obtain an angular ballistograph signal that is
indicative of rotational movement of a chest of a subject, and
signal processing means configured to generate from the angular
ballistocardiograph signal measured values of an output parameter
that is indicative of cardiac operation of the subject. These
elements may be implemented as one physical device, for example, a
mobile computing device, like a smartphone, or a tablet.
Alternatively, the elements may be included in two or more
electrically or communicatively coupled physical devices of the
system. FIG. 2 illustrates an exemplary configuration where the
system 200 comprises a sensor unit 202 and a control unit 204. In
this example, the sensor unit 202 may be considered as an element
to be attached to the monitored subject and the control unit 204
may be considered as an element physically detached from the
monitored subject.
[0034] The sensor unit 202 includes a sensor of angular motion 206.
The sensor of angular motion is configured to be attached to the
subject to move along motions of the subject, or part of the
subject it is attached to. Rotational movement or angular motion
refers herein to circular movement in which an object progresses in
radial orientation to a rotation axis. The sensor of angular motion
refers here to a functional element that may be exposed to angular
motion of the subject and translate at least one variable of the
angular motion into an electrical signal. Applicable variables
include, for example, position in radial orientation, angular
velocity and angular acceleration. Rotary motion of the heart and
the reverse rotary motion of the surrounding part of the body of
the subject are oscillatory, so the sensor of angular motion may be
configured to detect both direction and magnitude of an applied
variable.
[0035] The sensor unit 202 may also include a signal conditioning
unit 208 that manipulates the raw input electrical signal to meet
requirements of a next stage for further processing. Signal
conditioning may include, for example, isolating, filtering,
amplifying, and converting a sensor input signal to a proportional
output signal that may be forwarded to another control device or
control system. A signal conditioning unit 208 may also perform
some computation functions such as totalization, integration,
pulse-width modulation, linearization, and other mathematical
operations on a signal. The signal conditioning unit 208 may
alternatively be included in the control unit 204.
[0036] The sensor of angular motion is configured to generate a
chest motion signal, an angular ballistocardiograph signal that is
indicative of rotational recoil movement on the chest in response
to cardiac operation of the subject within the chest.
Ballistocardiography refers in general to a technology for
measuring movements of a body, which are caused in response to
shifts in the center of the mass of the body during heartbeat
cycles. The chest refers here to a pectoral part of the body in the
upper torso between the neck and the abdomen of the subject.
Advantageously, rotational movement of the chest about an axis
parallel to the sagittal plane of the subject is measured. However,
other axes may be applied within the scope, as well.
[0037] The sensor of angular motion 206 may be attached in a
desired position and orientation to the exterior of the chest of
the subject with a fastening element such that when the underlying
part of the chest moves, the sensor moves accordingly. The
fastening element refers here to mechanical means that may be
applied to position the sensor of angular motion 206 into contact
with the outer surface of the skin of the user. The fastening
element may be implemented, for example, with an elastic or
adjustable strap. The sensor of angular motion 206 and any
electrical wiring required by its electrical connections may be
attached or integrated to the strap. Other fastening mechanisms may
be applied, as well. For example the fastening element may comprise
one or more easily removable adhesive bands to attach the sensor of
angular motion 206 on the skin in the chest area. Rotational
movement of the chest of the subject may alternatively be detected
with a sensor of angular motion coupled to a position in any other
part of the upper torso of the subject. For example, a position in
the backside of the upper torso of the subject may be applied for
the purpose. Such sensor configuration allows measurements without
specific fastening elements. For example, the sensor unit may be
incorporated into an underlay, like a mattress on which the
monitored subject may lie without additional straps and tapes.
[0038] A sensor of angular motion typically has a sense direction,
which means that it is configured to sense angular motion about a
specific axis of rotation. This axis of rotation defines the sense
direction of the sensor of angular motion.
[0039] It is known that microelectromechanical (MEMS) structures
can be applied to quickly and accurately detect very small changes
in physical properties. A microelectromechanical gyroscope can be
applied to quickly and accurately detect very small angular
displacements. Motion has six degrees of freedom: translations in
three orthogonal directions and rotations around three orthogonal
axes. The latter three may be measured by an angular rate sensor,
also known as a gyroscope. MEMS gyroscopes use the Coriolis Effect
to measure the angular rate. When a mass is moving in one direction
and rotational angular velocity is applied, the mass experiences a
force in orthogonal direction as a result of the Coriolis force.
The resulting physical displacement caused by the Coriolis force
may then be read from, for example, a capacitively,
piezoelectrically or piezoresistively sensing structure.
[0040] In MEMS gyroscopes the primary motion is typically not
continuous rotation as in conventional ones due to lack of adequate
bearings. Instead, mechanical oscillation may be used as the
primary motion. When an oscillating gyroscope is subjected to an
angular motion orthogonal to the direction of the primary motion,
an undulating Coriolis force results. This creates a secondary
oscillation orthogonal to the primary motion and to the axis of the
angular motion, and at the frequency of the primary oscillation.
The amplitude of this coupled oscillation can be used as the
measure of the angular motion.
[0041] Being based on Coriolis force, the detected signal of a
gyroscope is minimally affected by gravity. This makes
gyrocardiograms far more insensitive to posture of the monitored
subject than, for example, seismocardiograms. The subject may then
freely select a comfortable position for taking a cardiogram
measurement, or to some extent even move during the
measurement.
[0042] During measurement the position of the sensor should
optimally be as close to the heart as possible and the orientation
of the sensor should be such that the sense direction is aligned as
accurately to the axis of rotation of the body of the subject as
possible. In a human subject, axes parallel to the sagittal plane
that passes from ventral to dorsal, and divides the body into
halves may be applied. These requirements for sensor positioning
are easy to understand and implement. The tolerances in positioning
are, in addition, reasonable, which enables fastening of the sensor
unit in, for example, ambulatory environment or by people with less
or no medical training.
[0043] Cardiac function typically includes various ventricular
directional motions of narrowing shortening, lengthening, widening
and twisting. Despite this directionality, it has been detected
that the recoil effect is relatively insensitive to the position
and orientation of the sensor unit. One reason for relative
insensitivity to deviations in the orientation is that in theory
the error is proportional to cosine of an angle between the sense
direction of the sensor and a rotation axis of the rotary
oscillation of the heart. It is known that in the neighborhood of
zero, cosine is a slowly decreasing function. One reason for
relative insensitivity to position of the sensor is that different
parts of the heart couple differently to the surrounding, mostly
liquid tissue. In addition, a volume of blood flowing into the
aorta contributes to the detected recoil motion of the chest. The
inertial volumes beyond the extent of the heart muscle itself
balance the recoil effect such that reasonable deviations in the
position and orientation of the sensor unit can be tolerated. In
addition, the detected motion is larger and thereby provides
relatively easily detectable large signals.
[0044] The control unit 204 is communicatively coupled to the
sensor unit to input signals generated by the sensor of angular
motion for further processing. Typically the coupling is
electrical, allowing both power supply to the sensor unit, as well
as wireline exchange of signals between the sensor unit and the
control unit. The sensor unit may, however, be a standalone unit
with own power supply and radio interface to the control unit. On
the other hand, the sensor unit and control unit may be implemented
as one integrated physical device.
[0045] The control unit 204 is a device that may comprise a
processing component 210. The processing component 210 is a
combination of one or more computing devices for performing
systematic execution of operations upon predefined data. The
processing component may comprise one or more arithmetic logic
units, a number of special registers and control circuits. The
processing component may comprise or may be connected to a memory
unit 212 that provides a data medium where computer-readable data
or programs, or user data can be stored. The memory unit may
comprise one or more units of volatile or non-volatile memory, for
example EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware, programmable
logic, etc.
[0046] The control unit 204 may also comprise, or be connected to
an interface unit 214 that comprises at least one input unit for
inputting data to the internal processes of the control unit, and
at least one output unit for outputting data from the internal
processes of the control unit.
[0047] If a line interface is applied, the interface unit 214
typically comprises plug-in units acting as a gateway for
information delivered to its external connection points and for
information fed to the lines connected to its external connection
points. If a radio interface is applied, the interface unit 214
typically comprises a radio transceiver unit, which includes a
transmitter and a receiver. A transmitter of the radio transceiver
unit may receive a bitstream from the processing component 210, and
convert it to a radio signal for transmission by an antenna.
Correspondingly, the radio signals received by the antenna may be
led to a receiver of the radio transceiver unit, which converts the
radio signal into a bitstream that is forwarded for further
processing to the processing component 210. Different line or radio
interfaces may be implemented in one interface unit.
[0048] The interface unit 214 may also comprise a user interface
with a keypad, a touch screen, a microphone, or equals for
inputting data and a screen, a touch screen, a loudspeaker, or
equals for outputting data to a user of the device.
[0049] The processing component 210 and the interface unit 214 are
electrically interconnected to provide means for performing
systematic execution of operations on the received and/or stored
data according to predefined, essentially programmed processes.
These operations comprise the procedures described herein for the
control unit of the monitoring system of FIG. 2.
[0050] FIG. 3 illustrates functional configuration of a cardiac
monitoring system 200 that includes the sensor unit 202 and the
control unit 204 of FIG. 2. The sensor unit, attached to the chest
of the monitored subject is exposed to temporary angular motion
AM.sub.chest of the chest, and undergoes a corresponding motion
am(t). In response to the angular motion am(t), the sensor unit
generates an angular ballistocardiograph signal S.sub.am and
forwards it to the control unit. The control unit includes one or
more data processing functions F.sub.1, F.sub.2, F.sub.3, each of
which defines a rule or correspondence between values of the
angular ballistocardiograph signal Sam and values of output
parameters p1, p2, p3 that are indicative of operational parameters
of the heart of the subject. The control unit may store one or more
of these output parameters p1, p2, p3 to a local data storage for
later processing, output one or more of them in one or more media
forms through the user interface of the control unit, or transmit
one or more of them to a remote node for further processing.
[0051] FIG. 4 illustrates another exemplary configuration where the
system 400 is a mobile computing device, a smartphone that
incorporates both the sensor unit and the control unit. Many of the
advanced mobile computing devices today include a gyroscope
apparatus, often a multi-axial gyroscope able to sense angular
motion in various directions. The signal or signals from the
internal gyroscope apparatus may be available, for example through
an application programming interface (API) of the operating system.
An application may be configured to use the gyroscope signals and
the computing means of the mobile computing device, and thereby
form the claimed system. The advantage of using a mobile computing
device system is that the monitoring can be made with a
non-dedicated device, typically available to the user in any case.
The user can easily use, for example, a smartphone to take his/her
own gyrocardiogram to, for example, measure heart rates, detect
atrial fibrillation etc. Furthermore, processing, memory and
interface means of the mobile computing device allow measured data
to be stored, preprocessed or processed locally in the mobile
computing device, and/or to be transmitted to a remote location for
further processing, or to be analyzed, for example by a
physician.
[0052] As will be discussed in more detail later on, in monitoring
systems the gyroscope signal may be used in combination with other
signal types. The mobile computing device of FIG. 4 may be equipped
with, for example, an ECG monitoring capability by integrating ECG
electrodes into a casing the mobile computing device. Such
configuration enables one to combine ECG and gyroscope signals to
determine, for example, cardiac time intervals.
[0053] As illustrated in FIG. 4, the mobile computing device 400
may also be connected with other apparatuses, such as a wrist-type
heart rate monitor 402 (smartwatch or similar) or a set of one or
two headphones 404 capable of measuring heart rates. The use of
signals from two measurement points makes it possible to determine
a pulse (arterial pressure pulse) transit time from the heart to
some specific position, in these exemplary cases to the wrist or to
the ear. When the distance between these two measurement positions
is known, the pulse transit time can be used to measure various
physiological parameters, such as blood pressure and arterial
resistance.
[0054] FIG. 5 illustrates measurement results taken with the system
of FIG. 4, i.e. with a smartphone attached to the chest of the
user. The smartphone includes also a multi-axial accelerometer, and
curves AccX, AccY, AccZ represent X- Y- and Z-direction signals
from the linear accelerometer. Curves GyroX, GyroY, GyroZ
representangular motion signals about X-, Y-, and Z-direction aces
from a gyroscope apparatus within the same smartphone. It may be
seen that the output signal of the multi-axial gyroscope is more
clear-cut and thus suitable for accurate analysis than the fuzzy
output signal of the multi-axial accelerometer.
[0055] FIG. 6 illustrates a remote monitoring system including the
cardiac monitoring system of FIG. 2. The system may include a local
node 600 that comprises the sensor unit 202 and the control unit
204 of FIG. 2. In addition, the local node 600 may be
communicatively connected to a remote node 602. The remote node 602
may be, for example, an application server that provides a
monitoring application as a service to one or more users. One of
the aspects monitored with the application may be the state of the
heart of the user. Alternatively, the remote node may be a personal
computing device into which a heart monitoring application has been
installed. The local node may be a dedicated device or combination
of devices including the sensor unit and the control unit described
above. Alternatively, the local node may be implemented as a sensor
unit that interfaces a client application in a multipurpose
computer device (for example a mobile phone, a portable computing
device, or network terminal of a user). A client application in the
computer device may interface the sensor unit and a server
application. The server application may be available in a physical
remote node 602, or in a cloud of remote nodes accessible through a
communication network.
[0056] While various aspects of the invention may be illustrated
and described as block diagrams, message flow diagrams, flow charts
and logic flow diagrams, or using some other pictorial
representation, it is well understood that the illustrated units,
blocks, apparatus, system elements, procedures and methods may be
implemented in, for example, hardware, software, firmware, special
purpose circuits or logic, a computing device or some combination
thereof. Software routines, which may also be called as program
products, are articles of manufacture and can be stored in any
apparatus-readable data storage medium, and they include program
instructions to perform particular predefined tasks. Accordingly,
embodiments of this invention also provide a computer program
product, readable by a computer and encoding instructions for
monitoring cardiac operations of a subject in a device or a system
of FIG. 2, 3, 4 or 5.
[0057] The sensor of angular motion is advantageously a
microelectromechanical device, but other angular motion detection
technologies may be applied, as well. For example, a magnetometer
attached to the chest of the subject may be used to determine the
change of position of the chest in relation to the earth's magnetic
field.
[0058] Noise and other unwanted features may be removed from the
raw angular ballistocardiograph signal S.sub.am with analog or
digital filters. A low pass, high pass or band pass filter may be
applied. For example, after converting the analog signal to digital
form, a digital low pass filter of the form
y(t)=(1-k)*y(t-1)+k*x(t) (1)
[0059] where
[0060] y(t)=value of the filtered signal at time step t,
[0061] y(t-1)=value of the filtered signal at time step (t-1),
[0062] x=value of the unfiltered signal at time step t,
[0063] k=filter coefficient,
[0064] may be applied for the purpose. The filtering may also or
alternatively apply polynomial fitting, for example convolution
with a Savitzky-Golay filter.
[0065] The curve of FIG. 7 illustrates an exemplary filtered
angular ballistocardiograph signal S.sub.am during heartbeat cycles
of a test subject. The vertical axis represents the magnitude of
sensed angular rate in the specific sense direction, and the
horizontal axis represents accumulated number of time steps or
elapsed time. Signal to noise ratio may be enhanced by means of
matched filtering, where the filtered signal is correlated to a
predefined template. The heart motion may be approximated to
constitute a reciprocating motion where the heart twists in a first
direction (here: positive twist), and in an opposite second
direction (here: negative twist). The template may comprise a set
of one or more limits for characteristics of the signal, for
example specific amplitude, time domain feature or frequency domain
feature.
[0066] As a simple example, matched filtering of the angular
ballistocardiograph signal S.sub.am of FIG. 7 may be done by means
of signal extreme (minimum/maximum) values. FIG. 8 shows a
simplified example of an angular ballistocardiograph signal
S.sub.am. For example, the control unit may be configured to
determine consecutive maximum and minimum values mx1, mn1, mx2,
mn2, mx3, mn3, . . . and determine slopes s1, s2, . . . between
them, as shown in FIG. 6.
s1=mx1-mn1
s2=mx2-mn1
s3=mx2-mn2
s4=mx3-mn2
[0067] etc.
[0068] The matched filtering template may include one or more
limits, for example, to maximum values, minimum values, the values
of individual slopes, or to a combination of slopes. FIG. 9
illustrates an exemplary output signal corresponding to the angular
ballistocardiograph signal S.sub.am of FIG. 7 after a specific
matched filtering, which will be discussed in more detail later
on.
[0069] The control unit may be configured to generate various
output parameters. In the simplest form, a parameter may be
indicative of radial orientation of the heart, angular velocity of
the heart, or angular acceleration of the heart during the twisting
motion. This output parameter may correspond to a measured,
conditioned, and filtered angular ballistocardiograph signal
S.sub.am shown in FIG. 7 or 9.
[0070] Alternatively, or additionally, a parameter may be
indicative of the stroke volume of the heart of the subject. The
output parameter may be generated by determining amplitude of the
angular ballistocardiograph signal S.sub.am and using that as a
value to represent the temporal stroke volume. For example, a peak
amplitude, semi-amplitude, or root mean square amplitude may be
used for the purpose. Since the signal is not a pure symmetric
periodic wave, amplitude is advantageously measured in respect to a
defined reference value, for example, from a zero point of the
signal curve. Other reference values may be applied within the
scope, as well.
[0071] Alternatively, or additionally, a parameter may be
indicative of the heartbeat of the subject. For example, the output
parameter may be generated by selecting a characteristic point of
the angular ballistocardiograph signal S.sub.am and determining the
occurrence of the characteristic point in consecutive signal
sequences. A minimum or maximum value of the signal sequence may be
applied as the characteristic point. The occurrence of the
characteristic point may be considered as a time stamp of the
heartbeat. A period between two timestamps may be considered to
represent temporary beat-to-beat (B-B) time of the heart of the
subject. The number of timestamps within a defined period may be
applied to indicate heart rate (HR) of the subject.
[0072] Alternatively, or additionally, a parameter may be
indicative of aortic opening or closing of the heart of the
subject. Aortic opening (AO) and aortic closing (AC) typically show
as peaks in the chest recoil effect. In measurement systems where
the recoil is measured with linear acceleration means, the AO and
AC peaks are quite similar in shape, but usually the AO peak is
higher than the AC peak. For some subjects, the AO peak and the AC
peak may, however, be almost as high, or the AC peak may even be
higher than the AO peak. Also, with linear acceleration means, the
posture of the subject tends to affect the shape of the signal. Due
to this, measurements with linear acceleration means do not
necessarily provide reliable data, especially if the subject may be
allowed to be in various postures. In measurement systems where the
recoil is measured by sensing angular motion with a gyroscope, the
AO peak has a very distinctive shape and is therefore much more
reliably distinguishable from the AC peak in the angular
ballistocardiograph signal S.sub.am.
[0073] Referring back to FIGS. 7 and 9, an emphasized section of
the angular ballistocardiograph signal S.sub.am in FIG. 7 includes
an AO peak that may be identified by means of matched filtering
mechanism described in general earlier. FIG. 10 illustrates a
potential AO peak from the signal of FIG. 5. In order to ensure
that a valid AO peak is detected, surroundings of the maximum
values of the angular ballistocardiograph signal S.sub.am may be
applied in the matched filtering template. For example, the control
unit may be configured to determine slopes of the signal curve, as
described above, and determine a sum of a defined number of
consecutive slopes. If the defined number is e.g. four, the control
unit could compute a sum S.sub.tot=s1+s2+s3+s4. A valid AO peak may
be considered, for example, to exist in the range that corresponds
to a maximum of sums S.sub.tot in the sequence.
[0074] Alternatively, or additionally, a parameter may be
indicative of another vital operation that interacts with the
cardiac function. Such vital operation can be, for example,
respiration. FIG. 11 illustrates exemplary values of stroke volume
and heartbeat timestamps in a signal measured from a test subject.
It may be seen that during respiration, the stroke volume and
beat-to-beat time of the heart typically change. When the lungs are
empty, the stroke volume may reach its maximum values, and the
beat-to-beat time may be lower. When the lungs are full, the stroke
volume values are smaller and the heart beats faster. Accordingly,
breathing of the subject may be seen as periodic modulation of the
angular ballistocardiograph signal S.sub.am. The frequency of the
modulation may be considered to represent the breathing rate of the
subject and the amplitude of the modulation may be considered to
represent the depth of the breathing of the subject.
[0075] Other parameters, derivable from the angular
ballistocardiograph signal Sam and applicable for representing
state of the cardiac functions of the subject may be used within
the scope, as well.
[0076] FIG. 12 illustrates measurements taken simultaneously from
one test subject with the two conventional technologies and with
the proposed new method. The first curve 10 shows an output signal
generated with an electrocardiogram, the second curve 12 shows an
output signal generated with a multi-axial accelerometer (a
seismocardiogram, z-axis) and the third curve 14 shows angular
ballistocardiograph signal generated with a multi-axial gyroscope
(y-axis). It may be seen that the occurrences related to aortic
valve opening AO (aortic rotational opening) are more
distinguishable in the proposed angular ballistocardiography signal
than in the multi-axial accelerometer signal.
[0077] One or more different types of output parameters may be
created in the system. These parameters may be output from the
system or applied in the system to indicate malfunctions and
abnormalities in cardiac operation of the subject.
[0078] In an embodiment, timing of two wave patterns that repeat on
the heart-beat rate of the subject may be applied to indicate
abnormal cardiac operation of the subject. For example, a first
signal indicative of electromagnetic phenomena related to cardiac
activity may be extracted from a first wave pattern that repeats on
a heart-beat rate. A second signal indicative of cardiovascular
rotation may be extracted from a second wave pattern that also
repeats on the heart-beat rate. The cardiovascular rotation may be
measured from the rotational movement of the chest of the subject,
as described above. The first signal and the second signal may be
used to form timing data, each timing value of which may be
indicative of a time period from a reference point of the first
wave pattern belonging to one heart-beat period to a reference
point of the second wave pattern belonging to the same heart-beat
period. Correlation between the timing data and pacing data
indicative of the heart-beat rate may be used as a parameter
indicative of cardiac (mal)function and (ab)normality.
[0079] The second wave pattern may be selected such that it
represents a response of the heart to the first wave pattern on the
first signal. The first signal can represent, for example, an
electrocardiograph ECG waveform. The first wave pattern can be, for
example but not necessarily, the R-peak of the ECG waveform shown
in FIG. 10, and the second wave pattern can be, for example but not
necessarily, the AO peak on the angular ballistocardiography
waveform shown in FIG. 12. In this case, the top of the R-peak can
be used as the reference point of the first wave pattern and the
top of the AO-peak can be used as the reference point of the second
wave pattern, and values of timing data TD can indicate the time
period from the moment of the top of the R-peak to the moment of
the top of the AO-peak.
[0080] The degree of correlation between the timing data and the
pacing data can be expressed, for example but not necessarily, with
the aid of a correlation coefficient that can be computed according
to the following equation:
C(j)=E{(TD-.mu..sub.T).times.(PD -.mu..sub.P)},
[0081] where C(j) is the correlation coefficient, E is the expected
value operator, i.e. E{variable} is the expected value of the
variable, TD is the timing data, .mu..sub.T is the mean of the
timing data, PD is the pacing data, .mu..sub.P is the mean of the
pacing data, and j is an integer expressing a time-lag of the
pacing data with respect to the timing data in heart-beat periods.
In light of empirical results, it is advantageous that the pacing
data PD has a lag of one heart-beat period with respect to the
timing data TD, i.e. j=1. In this case, when the timing data TD
relates to a given heart-beat period, the corresponding pacing data
PD relates to the previous heart-beat period. The correlation
coefficient can be expressed in a form .sigma..sub.T,P that it is
always on the range from -1 to +1:
.sigma..sub.T,P=C(j)/(.sigma..sub.T.times..sigma..sub.p),
[0082] where .sigma..sub.T and .sigma..sub.P are the standard
deviations of the timing data and the pacing data,
respectively.
[0083] FIG. 12 illustrates an exemplifying way to define the timing
data TD. In this exemplifying case, the R-peak appearing on the ECG
waveform and caused by depolarization of the ventricular muscle
tissue represents the first wave pattern 10 repeating on the
heart-beat rate, and the AO peak of the waveform indicative of
cardiovascular rotation represents the second wave pattern 14
repeating on the heart-beat rate. The top of the R-peak may be
applied as the reference point of the first wave pattern and the
top of the AO-peak may be applied as the reference point of the
second wave pattern.
[0084] It is to be noted that the given equation and the method for
defining the timing data are examples only. There are numerous ways
for expressing the possible correlation between the timing data and
the pacing data, and the present invention is not limited to a
particular way of expressing the correlation. Furthermore, it is to
be noted that the correlation is not necessarily a mathematical
quantity but it refers to any of a broad class of statistical
relationships involving dependence, and that the correlation in its
general sense does not imply or require causation.
[0085] As a specific example, FIG. 13 illustrates generation of a
parameter indicative of atrial extrasystole of the subject. The two
graphs in the left-hand side of FIG. 13 show the first wave pattern
10 and the second wave pattern 14, as introduced in FIG. 10. The
graph in the right side shows empirical values of the timing data
TD obtained from these wave patterns. Each number (1,2,3) in the
right-hand graph represents the time difference between the R-peak
of an ECG waveform in the first wave pattern 10 and the AO-peak of
a waveform indicative of cardiovascular rotation in the second wave
pattern 14. As can be seen from the left-hand graphs of FIG. 13,
the second beat 2 may be considered as atrial extrasystole, and the
first and the third beats may be considered normal. As shown in the
right-hand graph, the trend of the timing data increases during
atrial extrasystole, whereas in a normal case, the trend is
substantially constant or decreasing. A positive slope of in the
right-hand graph in FIG. 13 illustrates a positive correlation
between the timing data and the pacing data. A positive correlation
between the timing data and the pacing data may thus be applied in
or output from the system as a parameter indicative of atrial
extrasystole of the subject.
[0086] As another specific example, in light of empirical data, it
has been noticed that, during atrial fibrillation, there is
stochastic variation in the time delay (TD) between successive
heart-beat periods. FIG. 14 shows time differences (TD) between the
R-peak of an ECG waveform and the AO-peak of a waveform indicative
of cardiovascular rotation at different heart-beat rates in an
exemplifying case of atrial fibrillation of the subject.
[0087] The degree of the above-mentioned variation can be expressed
with the aid of a mathematical variation-quantity that can be
computed, for example, according to the following equation:
V = i = 1 M ( TD ( i ) - T ) 2 M - 1 T .times. 100 % ,
##EQU00001##
[0088] where V is the variation quantity, M is the number of timing
data values under consideration at the heart-beat rate under
consideration, and
T = i = 1 M TD ( i ) M . ##EQU00002##
[0089] In light of empirical data, the variation-quantity V can be
over 10% during atrial fibrillation and about 5% in a normal
case.
[0090] The system may thus be configured to produce a signal
expressing atrial fibrillation in response to a situation in which
the variation-quantity V is greater than a threshold. A suitable
value for the threshold can be determined on the basis of empirical
data gathered from a group of patients and/or other persons. The
threshold is not necessary a constant but the threshold can be
changing according to the individual under consideration, according
to time, and/or according to some other factors. It is also
possible to construct a series of thresholds where each threshold
represents a specific probability of atrial fibrillation or some
other cardiac malfunction and/or abnormality.
[0091] In another embodiment, amplitude variation, i.e. variation
of amplitude of a wave pattern repeating on the heart-beat rate on
the signal may be applied to indicate abnormal cardiac operation of
the subject. Amplitude variation may be detected from a signal
indicative of cardiovascular rotation. The amplitude variation may
be variation of amplitude of a wave pattern repeating on the
heart-beat rate on the signal so that the amplitude variation
includes a plurality of increases of the amplitude and a plurality
of decreases of the amplitude. An indicator of cardiac malfunction
and abnormality may, at least partly, be determined on the basis of
the detected amplitude variation. The above-mentioned wave pattern
can be, for example but not necessarily, the AO-peak of a waveform
indicative of cardiovascular rotation.
[0092] Such cardiac malfunctions and abnormalities, e.g. atrial
fibrillation, which may be sometimes challenging to diagnose, may
however cause irregularities on the waveform of the signal
indicative of cardiovascular rotation. These irregularities may be
difficult to detect from waveforms of one or two heart-beat periods
but they may manifest themselves in longer time periods covering
several heart-beat periods so that the amplitude of the wave
pattern repeating on the heart-beat rate varies more strongly than
in a normal case. Therefore, the amplitude variation represents
information indicative of cardiac malfunction and abnormality.
[0093] In another embodiment, time variation may be detected from
the signal, where the time variation is the variation of temporal
lengths of heart-beat periods. The indicator of cardiac malfunction
and abnormality can be determined on the basis of both the
amplitude variation and the time variation in order to improve the
reliability of the information indicative of cardiac malfunctions
and abnormalities.
[0094] FIG. 15 illustrates amplitude variation of an exemplifying
signal indicative of cardiovascular rotation over several
successive heartbeats in a case of atrial fibrillation when a
person under consideration is breathing. FIG. 16 illustrates an
example of an ECG waveform and an angular ballistocardiogram
waveform of an exemplifying signal indicative of cardiovascular
rotation.
[0095] The amplitude variation quantity may be applied as a
parameter indicative of cardiac operation and it can be compared to
a threshold in order to detect occurrence of cardiac malfunction
and abnormality. The threshold can be determined on the basis of
empirical data gathered from a group of patients and/or other
persons. The threshold is not necessary a constant but the
threshold can be changing according to the individual under
consideration, according to time, and/or according to some other
factors. It is also possible to construct a series of thresholds so
that each threshold represents a specific probability of atrial
fibrillation or some other cardiac malfunction and/or
abnormality.
[0096] The amplitude variation quantity can be, for example:
RMS.sub.p-p-AVE.sub.p-p,
[0097] where RMS.sub.p-p is the root-mean-square "RMS" of the
detected peak-to-peak values and AVE.sub.p-p is the arithmetic
average of the detected peak-to-peak values of the signal
indicative of cardiovascular rotation. For another example, the
strength of the amplitude variation can be expressed with the aid
of the standard deviation of the detected peak-to-peak values, i.e.
amplitude variation quantity can be the standard deviation of the
detected peak-to-peak values of the signal indicative of
cardiovascular rotation.
[0098] It is to be noted that there are numerous ways to express
the strength of the amplitude variation and the present invention
is not limited to any particular ways of expressing the strength of
the amplitude variation.
[0099] For added accuracy reliability and functionality it may,
however, be advantageous to use gyrocardiogram signals in
combination with signals generated through other measurement
technologies. For example, the angular ballistocardiograph signal
can be used in combination with conventional linear
ballistocardiologic (BCG) measurement data, dynamic and/or static
blood pressure measurement, Photoplethysmography (PPG), ultrasonic
or magnetic measurement equipment or ECG monitors. Combination of
the signals may be done in the control unit of the local node or in
a remote node of FIG. 6.
[0100] For early and efficient detection of anomalies in the
cardiac operation, angular ballistocardiograph signals of a subject
or parameter values generated from the angular ballistocardiograph
signals of the subject may be stored in a local or remote database.
The system may then be configured to automatically compare fresh
data to a selected piece of stored information, and create an alarm
if the deviation of new values from the stored information exceeds
a predefined threshold.
[0101] It is apparent to a person skilled in the art that as
technology advances, the basic idea of the invention can be
implemented in various ways. The invention and its embodiments are
therefore not restricted to the above examples, but they may vary
within the scope of the claims
* * * * *